Non-melanoma skin cancer is the most prevalent malignancy in the US, resulting in significant morbidity and health-care expense. Epidemiologic investigations have identified exposure to ultraviolet radiation as the primary risk factor for this disease; other environmental exposures that contribute to risk include ionizing radiation, arsenic, polycyclic aromatic hydrocarbons, and chronic immunosuppression. Host factors associated with increased risk for non-melanoma skin cancer include increasing age, male gender, and sun sensitive skin type. Basal cell and squamous cell carcinomas have been shown to contain alterations in the p53 gene, and recent work has identified a gene on chromosome 9q22, ptch, that is hypothesized to be critical in basal cell carcinoma tumorigenesis. These findings, while informative, are derived from relatively small, selected groups of patients and reflects the paucity of population-based molecular epidemiology for this disease. We propose to expand a large, well-established case-control study of non-melanoma skin cancer in New Hampshire to include investigation of genetic susceptibility. The project will focus on genes that potentially modify ultraviolet radiation exposure, including polymorphisms in the glutathione S-transferases (GSTM1, GSTT1, and GSTP1) and the newly identified variants in DNA excision repair genes (ERCC2/XPD, and XPF). In addition, we will collect tumor specimens from cases for characterization of mutations at p53 and 9q22/ptch. We will determine mutation spectra examine associations of mutation with carcinogenic exposures and patient traits, and refine a novel model of skin tumorigenesis. These studies will increase our understanding of host susceptibility to non-melanoma skin cancer and advance current models of skin carcinogenesis through identification of patterns of gene inactivation.